Support rand_mode in global constraint gathering (#6740) (#6752)

src/V3Randomize.cpp

@@ -882,20 +882,49 @@ class ConstraintExprVisitor final : public VNVisitor {
 
         VNRelinker relinker;
         nodep->unlinkFrBack(&relinker);
-        AstNodeExpr* exprp = new AstSFormatF{nodep->fileline(), smtName, false, nullptr};
+        AstNodeExpr* exprp;
         if (randMode.usesMode) {
-            AstNodeExpr* constFormatp = getConstFormat(nodep);
+            // Use string literal to avoid double formatting
-            UASSERT_OBJ(m_randModeVarp, nodep, "No m_randModeVarp");
+            exprp = new AstCExpr{nodep->fileline(), "std::string(\"" + smtName + "\")", 1};
-            AstCMethodHard* const atp = new AstCMethodHard{
+            exprp->dtypeSetString();
-                nodep->fileline(),
+
-                new AstVarRef{varp->fileline(), VN_AS(m_randModeVarp->user2p(), NodeModule),
+            // Get const format, using membersel if available for correct width/value
-                              m_randModeVarp, VAccess::READ},
+            AstNodeExpr* constFormatp
-                VCMethod::ARRAY_AT, new AstConst{nodep->fileline(), randMode.index}};
+                = membersel ? getConstFormat(membersel->cloneTree(false)) : getConstFormat(nodep);
+
+            // Build randmode access: for membersel, access parent object's __Vrandmode
+            AstNodeExpr* randModeAccess;
+            if (membersel) {
+                AstNodeExpr* parentAccess = membersel->fromp()->cloneTree(false);
+                AstNodeModule* const varClassp = VN_AS(varp->user2p(), NodeModule);
+                AstVar* const effectiveRandModeVarp = VN_AS(varClassp->user2p(), Var);
+                if (effectiveRandModeVarp) {
+                    AstMemberSel* randModeSel
+                        = new AstMemberSel{varp->fileline(), parentAccess, effectiveRandModeVarp};
+                    randModeSel->dtypep(effectiveRandModeVarp->dtypep());
+                    randModeAccess = randModeSel;
+                } else {
+                    UASSERT_OBJ(m_randModeVarp, nodep, "No m_randModeVarp");
+                    randModeAccess = new AstVarRef{varp->fileline(),
+                                                   VN_AS(m_randModeVarp->user2p(), NodeModule),
+                                                   m_randModeVarp, VAccess::READ};
+                }
+            } else {
+                UASSERT_OBJ(m_randModeVarp, nodep, "No m_randModeVarp");
+                randModeAccess
+                    = new AstVarRef{varp->fileline(), VN_AS(m_randModeVarp->user2p(), NodeModule),
+                                    m_randModeVarp, VAccess::READ};
+            }
+
+            AstCMethodHard* const atp
+                = new AstCMethodHard{nodep->fileline(), randModeAccess, VCMethod::ARRAY_AT,
+                                     new AstConst{nodep->fileline(), randMode.index}};
             atp->dtypeSetUInt32();
             exprp = new AstCond{varp->fileline(), atp, exprp, constFormatp};
-        } else if (!isGlobalConstrained) {
+            exprp->user1(true);  // Mark as formatted
-            // Non-global constraints: delete nodep immediately
+        } else {
-            VL_DO_DANGLING(pushDeletep(nodep), nodep);
+            exprp = new AstSFormatF{nodep->fileline(), smtName, false, nullptr};
+            if (!isGlobalConstrained) { VL_DO_DANGLING(pushDeletep(nodep), nodep); }
         }
         // else: Global constraints keep nodep alive for write_var processing
         relinker.relink(exprp);
@@ -952,7 +981,9 @@ class ConstraintExprVisitor final : public VNVisitor {
             methodp->addPinsp(varnamep);
             methodp->addPinsp(
                 new AstConst{varp->dtypep()->fileline(), AstConst::Unsized64{}, dimension});
-            if (randMode.usesMode) {
+            // Don't pass randMode.index for global constraints with membersel
+            // because constraint object can't access nested object's randmode array
+            if (randMode.usesMode && !(isGlobalConstrained && membersel)) {
                 methodp->addPinsp(
                     new AstConst{varp->fileline(), AstConst::Unsized64{}, randMode.index});
             }

test_regress/t/t_constraint_global_randMode.py

@@ -0,0 +1,21 @@
+#!/usr/bin/env python3
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2025 by Wilson Snyder. This program is free software; you
+# can redistribute it and/or modify it under the terms of either the GNU
+# Lesser General Public License Version 3 or the Perl Artistic License
+# Version 2.0.
+# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+import vltest_bootstrap
+
+test.scenarios('simulator')
+
+if not test.have_solver:
+    test.skip("No constraint solver installed")
+
+test.compile()
+
+test.execute()
+
+test.passes()

test_regress/t/t_constraint_global_randMode.v

@@ -0,0 +1,35 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain, for
+// any use, without warranty, 2025 by PlanV GmbH.
+// SPDX-License-Identifier: CC0-1.0
+
+class RandomValue;
+  rand int value;
+  constraint small_int_c {
+    value < 10;
+  }
+  task disable_val();
+    value.rand_mode(0);
+  endtask
+endclass
+
+class Base;
+  rand RandomValue v = new;
+endclass
+
+class Foo extends Base;
+endclass
+
+module t;
+  initial begin
+    Foo d = new;
+    Base b = d;
+    b.v.disable_val();
+    b.v.value = 11;
+    if (bit'(b.randomize())) $stop;
+    if (b.v.value != 11) $stop;
+    $write("*-* All Finished *-*\n");
+    $finish;
+  end
+endmodule